This invention relates to a solar collector. It relates more particularly to a panel-type solar collector that is particularly appropriate for hot water and space heating applications.
Due to the ever increasing costs of alternative energy sources, heating by solar energy is becoming more prevalent, particularly in homes. The panel-type solar collector with which this invention is particularly concerned, usually includes a large area, blackened absorber plate covered by one or more closely spaced coextensive transparent glass or plastic sheets which trap solar energy by reducing radiation and convection losses from the absorber plate.
The heat so collected is conducted to a fluid medium such as water in intimate thermal contact with the absorber plate. The heated medium is then circulated by a pump in an open loop system as is the case when heating water for a swimming pool. Alternatively, the medium can be circulated in a closed loop including a heat exchanger and used to heat fresh water for cooking or washing or to heat air for space heating purposes.
The factors that most effect the merchantability of solar collectors of this general type are cost, reliability, efficiency and ease of installation. There are many different types of solar collectors presently available. However, invariably these prior units are not entirely satisfactory with respect to one another of the aforesaid criteria.
Some prior collectors employ metal housings and frames for the absorber plates. Consequently, the panels as a whole are relatively heavy and massive, making them expensive to transport to the site and difficult to install. Other conventional panel constructions have absorber plate housings composed of different materials with different coefficients of thermal expansion. Consequently, when these panels are thermally cycled between their operating temperature extremes, cracks and gaps are formed between the various panel parts. Not only do these craks cause heat losses from panels, but they permit moisture to enter the panels. The mositure is deposited as a film on the interior surfaces of the covers inhibiting light transmission to the absorber plates and thereby reducing the overall heating efficiency of the panels.
Still other presently available collectors are designed so that they require a fixed configuation for the plumbing servicing the collectors. While this factor may not be a problem with new construction in which the plumbing can be routed as required, it does create installation difficulties when the panels are retrofitted to an existing building that imposes restraints on the plumbing routes.
Finally, most of the prior panel constructions are relatively expensive to make and install primarily because each panel comprises a relatively large number of parts. Thus, the materials costs are high, but also considerable labor is required to assemble the panels and install them at the site.